When Mitt Romney put Paul Ryan on the ticket, it had the potential to reset the presidential race - that is, offer a choice between two radically different visions of government, in a campaign seemingly stuck in tit-for-tat attacks over the economy. So far, though, the campaigns have a somewhat different fight on their hands. NPR's Mara Liasson reports.

MARA LIASSON, BYLINE: One thing the Ryan pick has done is force both campaigns to focus on Medicare, an issue that hasn't been front and center.

PRESIDENT BARACK OBAMA: I've proposed reforms that will save Medicare money by getting rid of wasteful spending in the healthcare system, reforms that will not touch your Medicare benefits, not by a dime.

LIASSON: President Obama, campaigning in Iowa yesterday, was responding to new attacks from the Romney campaign accusing him of cutting $716 billion from Medicare.

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UNIDENTIFIED MAN: Why? To pay for Obamacare. So now the money you paid for your guaranteed healthcare is going to a massive new government program that's not for you.

LIASSON: The Romney campaign's idea is to pit Obamacare, the massive new government program seniors in general don't like, against Medicare, the massive old government program they do like. But there was just one little problem with that strategy. Paul Ryan's budget also cuts Medicare by the same $716 billion, mostly to provider reimbursements. On CBS yesterday, Romney said that part of Ryan's plan was no longer operative.

MITT ROMNEY: Those cuts are going to be restored if I become president and Paul Ryan becomes vice president.

LIASSON: The Ryan pick was a 180 degree turn from Romney's original premise of the race, which was to focus exclusively on President Obama and the economy. And it's taken a while for the Romney campaign to adjust.

This week you could sometimes see the gears clunking awkwardly into place. First, Romney had to iron out the differences between his broad principles on the budget and Ryan's detailed blueprint. Then the campaign had to figure out what to do about Medicare. Weekly Standard editor Bill Kristol was one of the conservatives who pushed hard for Romney to pick Ryan.

BILL KRISTOL: The key move they made was to say, hey, let's have an Obamacare fight. Now Medicare's also potentially a Republican vulnerability, so it's not like, you know, either side's going to roll over for the other, but at least it's a fight.

LIASSON: Indeed, instead of rolling over, the Obama campaign is up on its hind legs begging for more. It sees a juicy opportunity in the Ryan plan, which would change Medicare from an insurance program that pays medical bills into a program where future seniors would get a fixed amount of money to buy private insurance. The Obama campaign released this web video featuring Florida seniors.

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UNIDENTIFIED WOMAN: It just doesn't make any sense to cut Medicare. It will be a voucher plan. If we cut it now, what's going to happen to our middle class?

LIASSON: Medicare has historically been a potent weapon for Democrats. But in 2010, many Republicans attacked the Medicare cuts in Obamacare and the GOP won 60 percent of elderly voters.

PAUL RYAN: The president, I'm told, is talking about Medicare today.

LIASSON: One Republican eager to try that again is Paul Ryan himself, who was campaigning in Ohio yesterday.

RYAN: We need this debate and we will win this debate.

LIASSON: Ryan followed the instructions sent out Monday by the National Republican Congressional Committee. Their memo told GOP candidates to never use the words privatize or entitlement reform. Instead it says say preserve, protect, strengthen or save.

RYAN: This is one area where this election presents such a clear contrast. Governor Romney and I will protect and strengthen Medicare for our current seniors and for our future seniors of tomorrow.

LIASSON: Republican pollster Matthew Dowd wonders if the Romney campaign is ready for a prolonged debate about Medicare.

MATTHEW DOWD: I don't get a sense for the next 70 days they want to make this about entitlements and about the fiscal problem in Washington and about the budget. I don't get a sense they want to change their whole strategy to a discussion of that when that issue isn't even in the top three or four issues in the country right now.

LIASSON: But that's the debate that you get when you put Paul Ryan on the ticket. And how this new debate about fiscal policy plays out will help answer another question - was putting Paul Ryan on the ticket a smart move or not? GOP strategist Ed Rogers.

ED ROGERS: It certainly filled the news hole. Nobody's chasing Romney around about his tax returns right now. It's all about Ryan. So, so far he's served a worthwhile purpose. But my history is the vice presidential nominees after being shot out of a cannon fade pretty quickly. And so is Ryan going to follow that path or is something new happening? I think the jury's still out on that.

LIASSON: The Ryan pick has given a jolt of excitement to the Romney campaign, and it's given the presidential race a chance to be about something bigger than personal attacks. The next few weeks will determine whether this unusual move, where the nominee essentially adopts the vision of his number two, was more risk or reward.